Gas chromatography requires the preparation of controlled gas-vapor mixtures for the purpose of calibration and analysis. This procedure involves the introduction of a precise volume of liquid into a chamber containing a carrier gas of known properties, the liquid being instantly vaporized to form a gas-vapor mixture. Typically this procedure is carried out by manual injection using micro-syringes. There are obvious disadvantages to this procedure in that it requires a practiced hand to fill the syringe with a bubble-free sample and then inject repetitively so that consistent results are achieved. Both the calibration standard and the sample must be injected several times to ensure accurate results.
In a syringe there must be perfect sealing between the plunger or piston and the barrel along its entire length. This becomes a problem, particularly, in micro-syringes where the plunger is a very thin rod that can bend or deform easily after short usage.
The same criteria for standard and sample delivery into the chamber apply to high performance liquid chromatography. In some ways the procedure is more arduous in that samples must be degassed, and more care is required because of large sample volumes and larger syringes.
It is therefor an object of this invention to provide a liquid dispensing device which overcomes or at least minimizes these problems and provides repeatable delivery of a gas free sample.